Reusing multiple contexts in Python 'with' statement
0
In Python3 we can use multiple contexts in with statements. But is it possible to enter multiple contexts if they can't be constructed right away in the with statement? Is it possible to do something like this?
def files():
return open('a.txt', 'w'), open('b.txt', 'w')
with files():
pass
Or this:
files = open('a.txt', 'w'), open('b.txt', 'w')
with files:
pass
python python-3.x with-statement
asked Nov 15 at 22:53
DikobrAz
1,6572038
add a comment |
0
In Python3 we can use multiple contexts in with statements. But is it possible to enter multiple contexts if they can't be constructed right away in the with statement? Is it possible to do something like this?
def files():
return open('a.txt', 'w'), open('b.txt', 'w')
with files():
pass
Or this:
files = open('a.txt', 'w'), open('b.txt', 'w')
with files:
pass
python python-3.x with-statement
asked Nov 15 at 22:53
DikobrAz
1,6572038
1
That's an unsafe pattern - if something goes wrong while opening the second file, the first doesn't get closed. If you give more detail about why you're trying to do this, we can probably give you a better option. (ExitStack is likely to be involved.)
– user2357112
Nov 15 at 23:00
1
@user2357112 yeah... was going to suggest having a look atcontextlib.ExitStackas that's my gut feeling but I'm still not sure what the use case is...
– Jon Clements♦
Nov 15 at 23:02
Is there a way to make it safe, e.g. to replicate the behavior ofwith open(...), open().... Maybe saving context into variable is not nice, but pattern with a function should be fairy safe.
– DikobrAz
Nov 15 at 23:04
add a comment |
0
0
0
In Python3 we can use multiple contexts in with statements. But is it possible to enter multiple contexts if they can't be constructed right away in the with statement? Is it possible to do something like this?
def files():
return open('a.txt', 'w'), open('b.txt', 'w')
with files():
pass
Or this:
files = open('a.txt', 'w'), open('b.txt', 'w')
with files:
pass
python python-3.x with-statement
asked Nov 15 at 22:53
DikobrAz
1,6572038
In Python3 we can use multiple contexts in with statements. But is it possible to enter multiple contexts if they can't be constructed right away in the with statement? Is it possible to do something like this?
def files():
return open('a.txt', 'w'), open('b.txt', 'w')
with files():
pass
Or this:
files = open('a.txt', 'w'), open('b.txt', 'w')
with files:
pass
python python-3.x with-statement
python python-3.x with-statement
asked Nov 15 at 22:53
DikobrAz
1,6572038
asked Nov 15 at 22:53
DikobrAz
1,6572038
asked Nov 15 at 22:53
DikobrAz
1,6572038
asked Nov 15 at 22:53
DikobrAz
1,6572038
asked Nov 15 at 22:53
DikobrAz
1,6572038
1,6572038
1
That's an unsafe pattern - if something goes wrong while opening the second file, the first doesn't get closed. If you give more detail about why you're trying to do this, we can probably give you a better option. (ExitStack is likely to be involved.)
– user2357112
Nov 15 at 23:00
1
@user2357112 yeah... was going to suggest having a look atcontextlib.ExitStackas that's my gut feeling but I'm still not sure what the use case is...
– Jon Clements♦
Nov 15 at 23:02
Is there a way to make it safe, e.g. to replicate the behavior ofwith open(...), open().... Maybe saving context into variable is not nice, but pattern with a function should be fairy safe.
– DikobrAz
Nov 15 at 23:04
add a comment |
1
That's an unsafe pattern - if something goes wrong while opening the second file, the first doesn't get closed. If you give more detail about why you're trying to do this, we can probably give you a better option. (ExitStack is likely to be involved.)
– user2357112
Nov 15 at 23:00
1
@user2357112 yeah... was going to suggest having a look atcontextlib.ExitStackas that's my gut feeling but I'm still not sure what the use case is...
– Jon Clements♦
Nov 15 at 23:02
Is there a way to make it safe, e.g. to replicate the behavior ofwith open(...), open().... Maybe saving context into variable is not nice, but pattern with a function should be fairy safe.
– DikobrAz
Nov 15 at 23:04
1
1
That's an unsafe pattern - if something goes wrong while opening the second file, the first doesn't get closed. If you give more detail about why you're trying to do this, we can probably give you a better option. (ExitStack is likely to be involved.)
– user2357112
Nov 15 at 23:00
That's an unsafe pattern - if something goes wrong while opening the second file, the first doesn't get closed. If you give more detail about why you're trying to do this, we can probably give you a better option. (ExitStack is likely to be involved.)
– user2357112
Nov 15 at 23:00
1
1
@user2357112 yeah... was going to suggest having a look at
contextlib.ExitStack as that's my gut feeling but I'm still not sure what the use case is...– Jon Clements♦
Nov 15 at 23:02
@user2357112 yeah... was going to suggest having a look at
contextlib.ExitStack as that's my gut feeling but I'm still not sure what the use case is...– Jon Clements♦
Nov 15 at 23:02
Is there a way to make it safe, e.g. to replicate the behavior of
with open(...), open().... Maybe saving context into variable is not nice, but pattern with a function should be fairy safe.– DikobrAz
Nov 15 at 23:04
Is there a way to make it safe, e.g. to replicate the behavior of
with open(...), open().... Maybe saving context into variable is not nice, but pattern with a function should be fairy safe.– DikobrAz
Nov 15 at 23:04
add a comment |
2 Answers
2
active
oldest
votes
2
from contextlib import contextmanager
@contextmanager
def files():
with open('a.txt', 'w') as f1, open('b.txt', 'w') as f2:
yield f1,f2
maybe?
with files() as (f1,f2):
print(f1,f2)
answered Nov 15 at 22:59
Joran Beasley
72.2k677116
But then you're returning two closed files.
– user2357112
Nov 15 at 23:00
1
I think you're missing@contextlib.contextmanagernow.
– user2357112
Nov 15 at 23:02
1
Also parentheses around thef1,f2inwith files() as f1,f2, or the precedence isn't going to work the way you want.
– user2357112
Nov 15 at 23:03
lol thanks :P ..
– Joran Beasley
Nov 15 at 23:03
add a comment |
2
An example using contextlib.ExitStack:
from contextlib import ExitStack
def files(stack, *args):
return [stack.enter_context(open(f, "w")) for f in args]
with ExitStack() as stack:
f1, f2 = files(stack, "a.txt", "b.txt")
...
or without the wrapper
with ExitStack() as stack:
f1, f2 = [stack.enter_context(open(f, "w")) for f in ["a.txt", "b.txt"]]
...
However, when you know how many files are to be opened ahead of time (and it's a small number of files), the multiple manager form of the with statement as shown in Joran Beasley's answer is simpler.
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
2
from contextlib import contextmanager
@contextmanager
def files():
with open('a.txt', 'w') as f1, open('b.txt', 'w') as f2:
yield f1,f2
maybe?
with files() as (f1,f2):
print(f1,f2)
answered Nov 15 at 22:59
Joran Beasley
72.2k677116
But then you're returning two closed files.
– user2357112
Nov 15 at 23:00
1
I think you're missing@contextlib.contextmanagernow.
– user2357112
Nov 15 at 23:02
1
Also parentheses around thef1,f2inwith files() as f1,f2, or the precedence isn't going to work the way you want.
– user2357112
Nov 15 at 23:03
lol thanks :P ..
– Joran Beasley
Nov 15 at 23:03
add a comment |
2
from contextlib import contextmanager
@contextmanager
def files():
with open('a.txt', 'w') as f1, open('b.txt', 'w') as f2:
yield f1,f2
maybe?
with files() as (f1,f2):
print(f1,f2)
answered Nov 15 at 22:59
Joran Beasley
72.2k677116
But then you're returning two closed files.
– user2357112
Nov 15 at 23:00
1
I think you're missing@contextlib.contextmanagernow.
– user2357112
Nov 15 at 23:02
1
Also parentheses around thef1,f2inwith files() as f1,f2, or the precedence isn't going to work the way you want.
– user2357112
Nov 15 at 23:03
lol thanks :P ..
– Joran Beasley
Nov 15 at 23:03
add a comment |
2
2
2
from contextlib import contextmanager
@contextmanager
def files():
with open('a.txt', 'w') as f1, open('b.txt', 'w') as f2:
yield f1,f2
maybe?
with files() as (f1,f2):
print(f1,f2)
answered Nov 15 at 22:59
Joran Beasley
72.2k677116
from contextlib import contextmanager
@contextmanager
def files():
with open('a.txt', 'w') as f1, open('b.txt', 'w') as f2:
yield f1,f2
maybe?
with files() as (f1,f2):
print(f1,f2)
answered Nov 15 at 22:59
Joran Beasley
72.2k677116
edited Nov 15 at 23:03
answered Nov 15 at 22:59
Joran Beasley
72.2k677116
answered Nov 15 at 22:59
Joran Beasley
72.2k677116
answered Nov 15 at 22:59
Joran Beasley
72.2k677116
72.2k677116
But then you're returning two closed files.
– user2357112
Nov 15 at 23:00
1
I think you're missing@contextlib.contextmanagernow.
– user2357112
Nov 15 at 23:02
1
Also parentheses around thef1,f2inwith files() as f1,f2, or the precedence isn't going to work the way you want.
– user2357112
Nov 15 at 23:03
lol thanks :P ..
– Joran Beasley
Nov 15 at 23:03
add a comment |
But then you're returning two closed files.
– user2357112
Nov 15 at 23:00
1
I think you're missing@contextlib.contextmanagernow.
– user2357112
Nov 15 at 23:02
1
Also parentheses around thef1,f2inwith files() as f1,f2, or the precedence isn't going to work the way you want.
– user2357112
Nov 15 at 23:03
lol thanks :P ..
– Joran Beasley
Nov 15 at 23:03
But then you're returning two closed files.
– user2357112
Nov 15 at 23:00
But then you're returning two closed files.
– user2357112
Nov 15 at 23:00
1
1
I think you're missing
@contextlib.contextmanager now.– user2357112
Nov 15 at 23:02
I think you're missing
@contextlib.contextmanager now.– user2357112
Nov 15 at 23:02
1
1
Also parentheses around the
f1,f2 in with files() as f1,f2, or the precedence isn't going to work the way you want.– user2357112
Nov 15 at 23:03
Also parentheses around the
f1,f2 in with files() as f1,f2, or the precedence isn't going to work the way you want.– user2357112
Nov 15 at 23:03
lol thanks :P ..
– Joran Beasley
Nov 15 at 23:03
lol thanks :P ..
– Joran Beasley
Nov 15 at 23:03
add a comment |
2
An example using contextlib.ExitStack:
from contextlib import ExitStack
def files(stack, *args):
return [stack.enter_context(open(f, "w")) for f in args]
with ExitStack() as stack:
f1, f2 = files(stack, "a.txt", "b.txt")
...
or without the wrapper
with ExitStack() as stack:
f1, f2 = [stack.enter_context(open(f, "w")) for f in ["a.txt", "b.txt"]]
...
However, when you know how many files are to be opened ahead of time (and it's a small number of files), the multiple manager form of the with statement as shown in Joran Beasley's answer is simpler.
add a comment |
2
An example using contextlib.ExitStack:
from contextlib import ExitStack
def files(stack, *args):
return [stack.enter_context(open(f, "w")) for f in args]
with ExitStack() as stack:
f1, f2 = files(stack, "a.txt", "b.txt")
...
or without the wrapper
with ExitStack() as stack:
f1, f2 = [stack.enter_context(open(f, "w")) for f in ["a.txt", "b.txt"]]
...
However, when you know how many files are to be opened ahead of time (and it's a small number of files), the multiple manager form of the with statement as shown in Joran Beasley's answer is simpler.
add a comment |
2
2
2
An example using contextlib.ExitStack:
from contextlib import ExitStack
def files(stack, *args):
return [stack.enter_context(open(f, "w")) for f in args]
with ExitStack() as stack:
f1, f2 = files(stack, "a.txt", "b.txt")
...
or without the wrapper
with ExitStack() as stack:
f1, f2 = [stack.enter_context(open(f, "w")) for f in ["a.txt", "b.txt"]]
...
However, when you know how many files are to be opened ahead of time (and it's a small number of files), the multiple manager form of the with statement as shown in Joran Beasley's answer is simpler.
An example using contextlib.ExitStack:
from contextlib import ExitStack
def files(stack, *args):
return [stack.enter_context(open(f, "w")) for f in args]
with ExitStack() as stack:
f1, f2 = files(stack, "a.txt", "b.txt")
...
or without the wrapper
with ExitStack() as stack:
f1, f2 = [stack.enter_context(open(f, "w")) for f in ["a.txt", "b.txt"]]
...
However, when you know how many files are to be opened ahead of time (and it's a small number of files), the multiple manager form of the with statement as shown in Joran Beasley's answer is simpler.
answered Nov 15 at 23:13
community wiki
chepner
add a comment |
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1
That's an unsafe pattern - if something goes wrong while opening the second file, the first doesn't get closed. If you give more detail about why you're trying to do this, we can probably give you a better option. (ExitStack is likely to be involved.)
– user2357112
Nov 15 at 23:00
1
@user2357112 yeah... was going to suggest having a look at
contextlib.ExitStackas that's my gut feeling but I'm still not sure what the use case is...– Jon Clements♦
Nov 15 at 23:02
Is there a way to make it safe, e.g. to replicate the behavior of
with open(...), open().... Maybe saving context into variable is not nice, but pattern with a function should be fairy safe.– DikobrAz
Nov 15 at 23:04